Conflate

Wiktionary's definition of "simplistic" includes this usage note: "This is not to be conflated with “simple”. simplistic implies simplicity to excess, whereas simple does not. The phrase “overly simplistic” is therefore a tautology."

Conflate is a good word to keep in one's vocabulary, one's mental toolbelt. Merriam-Webster defines it as follows:

1 a: to bring together : fuse b: confuse
2: to combine (as two readings of a text) into a composite whole

In the case of simple vs. "simplistic", it's an error, of course. At the same time, it echoes Ayn Rand's reminder about the importance of the precise use of language—the primary purpose of which is precise understanding, the growth of your own personal knowledge. It aids communication, of course; but first and foremost, understand well what it is you wish to communicate.

The precise use of language is aided by knowing about something Rand called package-dealing". The arch example of a package-deal is the word selfishness, how it is commonly used. Ayn Rand writes of it as follows (from her nonfiction book, The Virtue of Selfishness):

The title of this book may evoke the kind of question that I hear once in a while: "Why do you use the word 'selfishness' to denote virtuous qualities of character, when that word antagonizes so many people to whom it does not mean the things you mean?" To those who ask it, my answer is: "For the reason that makes you afraid of it." But there are others, who would not ask that question, sensing the moral cowardice it implies, yet who are unable to formulate my actual reason or to identify the profound moral issue involved. It is to them that I will give a more explicit answer.

It is not a mere semantic issue nor a matter of arbitrary choice. The meaning ascribed in popular usage to the word "selfishness" is not merely wrong: it represents a devastating intellectual "package-deal," which is responsible, more than any other single factor, for the arrested moral development of mankind. In popular usage, the word "selfishness" is a synonym of evil; the image it conjures is of a murderous brute who tramples over piles of corpses to achieve his own ends, who cares for no living being and pursues nothing but the gratification of the mindless whims of any immediate moment. Yet the exact meaning and dictionary definition of the word "selfishness" is: concern with one's own interests. This concept does not include a moral evaluation; it does not tell us whether concern with one's own interests is good or evil; nor does it tell us what constitutes man's actual interests. It is the task of ethics to answer such questions.

The lesson I take from that is this—precision matters, not just in my particular profession, but most particularly in my personal life, in all my relationships from casual to intimate. The precise use of words helps me to enjoy and honor those relationships at the same time. When I call or regard someone as either selfless or selfish, I use those words with absolute precision. Paradoxically, that razor sharp mental focus makes it all the easier for me to enjoy my emotions, my happy responses to those closest to me. For more details, for now, I refer you to the corpus of Ayn Rand's works.